This invention relates to a radianted noise measurement apparatus and a radiated noise measurement method for measuring radiated noise generated from an electronic unit, etc., such as a product containing electronic parts for one or more printed circuit boards on which electronic parts are installed, on which measurement is to be made, a radiated noise display method, and a radiated noise detection apparatus.
A three-dimensional interference measurement apparatus described in the Unexamined Japanese Patent Application Publication Nos. Hei 6-58969, and Hei 6-58970 is proposed, for example, as an unnecessary radiated noise measurement apparatus on a printed-circuit board on which electronic parts are installed. It measures radiated noise generated from a printed-circuit board and comprises a plane sensor being placed in a table for detecting noise on an X-Y plane from the rear of the printed-circuit board and a magnetic field sensor being mounted on the printed-circuit board for measuring noise in the Z axis direction of the surface of the printed-circuit board.
The three-dimensional interference measurement apparatus makes measurement only on printed-circuit boards and cannot cover objects having a curved surface. Printed-circuit boards which provide full functions singly are few; generally many printed-circuit boards are configured to transfer a signal and power to and from other electronic parts or printed-circuit boards via a wire harness in input, output, power supply, etc. Radianted noise is classified into differential mode noise and common mode noise. The level of the common mode noise mainly caused by a high-frequency current flowing into a harness because of the potential difference between power supply and ground in a board or between boards in a system is far higher than the level of the differential mode noise generated due to board wiring, etc. Steps for decreasing the common mode noise are taken, thereby producing a large effect as countermeasures against noise. However, the above-described three-dimensional interference measurement apparatus cannot evaluate noise in the whole system.
In contrast, a radio wave source visualizing apparatus described in the Unexamined Japanese Patent Application Publication No. Hei 6-94763 adopts a method of finding reception output while moving a horizontally polarized wave reception antenna and a vertically polarized wave reception antenna in X-Y coordinates of an observation plane and comparing the reception output with reception output of a fixed antenna placed near the observation plane as a measurement method of unnecessary radiated noise generated from a product containing printed-circuit boards and electronic parts.
The method takes time in moving the horizontally polarized wave reception antenna and the vertically polarized wave reception antenna and inputting data and cannot deal with instantaneously occurring noise. Consideration is not given to an antenna moving method if the observation plane has a complicated curved face. Generally, there is an inverse square relationship between electric field strength and distance according to Coulomb's law and distance change causes an error to occur, thus the distance between the observation plane and measurement point needs to be made constant for making measurement.
FIG. 13 is a schematic representation of a conventional measurement method using a fixed antenna. In the figure, numeral 60 is a product provided for testing, numeral 61 is a turn table, numeral 62 is a direct wave, numeral 63 is a reflected wave, numeral 64 is a fixed antenna, numeral 65 is a switch section, numeral 66 is a receiver, and numeral 67 is a spectrum analyzer. The product 60 is placed on the turn table 61. While it is turned, noise is caught at the fixed antenna 64 and is measured with the receiver 66 or the spectrum analyzer 67 selected by means of the switch section 65. The distance between the product 60 and the fixed antenna 64 is 3 m or 10 m and further the effects of the direct wave 62 and the reflected wave 63 are received, thus fine evaluation cannot be performed. Since the rotation of the turn table on which the product is placed cannot be speeded up, the measurement method cannot deal with instantaneously occurring noise.
Thus, the above-described measurement system requires large-scale facilities and is expensive. In contrast, a method of connecting a non-contact high-frequency probe to a spectrum analyzer and making simple measurement is conducted generally. However, in this method, it is hard to keep the distance between the non-contact high-frequency probe and the spectrum analyzer constant and different data is provided each time measurement is made, namely, repeatability presents a problem.
Further, a problem common to the related arts is that if a radiated noise generation source can be located, a high-frequency current flow therefrom cannot be estimated. Therefore, to take countermeasures against noise, estimation of a cause from information provided by the conventional measurement system depends greatly on the technique proper to the engineer.
Since it takes time in evaluation at volume production, a sampling inspection is executed, but it is not guaranteed that unsampled ones of products varying in a wide range are within the specs; a 100 percent inspection is desired.